Ironing may be described as the process of using an iron to remove wrinkles from a fabric, in particular a garment. During ironing, the fabric may preferably be heated to loosen the intermolecular bonds between the long-chain polymer molecules in the fibers of the fabric. In their loosened condition the weight of the iron may force the fibers in a wrinkle-free state. When the stress in the fibers is properly removed the wrinkle-free state of the fabric will be maintained upon cooling. The removal of stress in the fibers of the fabric is significantly enhanced by heating the fabric to above its glass transition temperature. For many natural fabrics, such as cotton, wool and linen, the glass transition temperature is dependent on the moisture content. The dependency is such that an increase in the moisture content or humidity lowers the transition temperature. A higher moisture content thus improves the degree of stress relaxation, and hence the ironing result at the same temperature. To achieve optimum ironing results, a moisture content of about 3-15% by weight of the fabric to be ironed is desired. The precise optimum percentage depends on the nature of the fabric, and may for example be relatively low for polyester while it is relatively high for natural materials such as cotton.
A fabric to be ironed may be moisturized in several ways.
A steam iron uses steam to moisturize a fabric. The steam is normally released through steam outlet openings in the heated soleplate of the iron, and moisturizes the fabric by subsequently condensing therein. A significant drawback of this approach is that steam is not a very efficient moisturizer: only a small fraction of the steam, typically on the order of several tens of percent, is used for moisturizing the fabric; the rest passes through it without condensing. The percentage of the steam that passes through the fabric even increases as the temperature of the fabric rises during ironing, simply because less steam condenses at higher temperatures. When the fabric reaches a temperature of 100° C. or above, no steam condensation occurs at all. This implies that steam irons are rather wasteful with both water and the energy required to evaporate it. Furthermore, steam irons are generally incapable of effecting the aforementioned optimum moisture content in the fabric.
U.S. Pat. No. 6,035,563 (Hoefer et al.) discloses an electric iron that moistens a fabric being ironed by means of liquid water. To this end the soleplate of the iron is provided with at least one water outlet opening, arranged in an area of the soleplate tip. The water outlet opening allows a liquid stored in a liquid tank to pass through and moisten materials to be ironed. The liquid exits the opening in the form of liquid droplets that are generated using a piezoelectric excitation atomizer device above the soleplate. The iron disclosed by U.S. '563 is capable of moisturizing a fabric up to the optimum moisture content. However, in doing so it may leave behind wet spots, i.e. a patch of fabric that has been moistened but incompletely dried thereafter, such that it is visibly left behind once the ironing stroke over said portion has ended. This is undesirable because it requires a user to check for wet spots, and to ‘mop up’ any when found by moving the iron over it as long as it takes for the heated soleplate to evaporate them.